The strategy for implementing damage detection and the characterization of mechanical structures is commonly called Structural Health Monitoring (SHM). Damages are defined as modifications of the material and/or of the geometrical properties of a structural system, comprising modifications of boundary conditions and connections of the system, that worsen performance of the system. The SHM process implies the observation of the mechanical system over time using periodically: measurements of dynamic responses coming from an array of sensors, extraction of data of damage characteristics sensed from these measurements, and statistical analysis of these data of damage characteristics for determining the present health state of the system (also called structural analysis).
This process provides information about the capacity of the structure for carrying out its function, considering the unavoidable aging and degradation in working environments. After extreme events, such as earthquakes or explosions, the SHM is used for a quick screening of the conditions of the structure for providing, almost in real time, reliable information about the integrity of the structure itself.
Currently, SHM systems use sensors placed on the surfaces to be monitored. For example, sensors used (anemometers for calculating the wind speed, accelerometers, extensometers, motion transducers, temperature sensors, sensors for detecting motion of weights, etc.) for monitoring bridges are placed on the external surfaces of beams, ropes or pillars. This is done to: estimate the effects of loads on the bridge, evaluate the weakening of the bridge, and foresee the probable evolution of the bridge and its expected lifetime.
SHM systems with sensors to be buried in the building structure to be monitored have been devised. These sensors (pressure, humidity, temperature, etc.) have at least one remote powering and transmission antenna for transmitting the measured values outside of the block of building material. These kinds of sensors are disclosed, for example, in U.S. patent application No. 2004/0153270 and in Italian patent applications VA2010A000097 and MI2010A002365.
An inconvenience of the monitoring circuits to be buried in the building material includes the difficulties of powering them. In Italian patent application No. VA2010A000097, each monitoring circuit is powered through a magnetic coupling with an inductor connected to a shielded line, as shown in FIG. 1. In Italian patent application No. MI2010A002365 the monitoring circuits are fixed to a linear support, as shown in FIG. 2, and have remote powering antennas that receive the electromagnetic field irradiated by an external power supply.